Lead-coated article for industrial operations in acidic medium

ABSTRACT

Techniques described herein relate to an article, including an electrolytic tank for refining metals, and related production techniques, wherein the article defines a channel or cavity receiving a corrosive medium including sulfuric acid. The article includes a corrosion-resistant lead coating including at least one layer of lead solidified onto at least a portion of the cavity. The corrosion-resistant coating can be combined with additional layers including fiberglass-based material for further protection against corrosion.

TECHNICAL FIELD

The technical field generally relates to designing a corrosion-resistant article to handle industrial operations in an acidic medium, and more particularly to a hydrometallurgical tank including at least one protective layer of lead.

BACKGROUND

In the hydrometallurgical industry, it is of common practice to refine metal by electrolysis in electrolytic cells especially designed for this purpose. The metals to be refined are usually conventional non-ferrous metals like copper, zinc, nickel, cobalt, tin, lead, manganese or cadmium, or precious metals like silver, platinum, gold, rare earths and others.

Hydrometallurgical processes make use of electrolytic tanks for refining the metals with multiple rows of electrodes plunged in an acidic electrolytic bath contained in the electrolytic tank. Materials of the electrolytic tank must therefore stand up to highly corrosive conditions of the acidic electrolytic bath and heavy weight of the electrodes.

Known materials used to design an electrolytic tank includes composite materials such as polymer concrete, fiberglass and other corrosion-resistant polymers, or metallic tanks covered with a plastic liner. Published US Patent Application No. 2018/0148852 describes an electrolytic tank having a core made of concrete polymer, and a reinforcing multiple-layer fiberglass-based envelope. The envelope includes an anti-corrosive inner hull and a reinforced outer hull. The first two innermost layers of the inner hull are made of “gel coat” (such as pure resin with little chemical additives) to obtain optimal corrosion resistance (i.e. against sulfuric acid and/or Cl2 and/or Cl—, chlorine) and the following layers are made of an anticorrosive fiberglass coat (such as type A or Type C fiberglass), and a synthetic fiber veil (such as polyester).

However, tank walls covered with plastic anti-corrosive layers (such as a thermoset resin of vinyl ester and fibers of fiberglass) can absorb a certain amount of water. A part the water can be absorbed by the resin, and another part can also be absorbed at the interface between the fibers and the resin. During hydrometallurgical operations, absorbed water is gradually replaced by the acid or base contained in the electrolytic bath. For example, sulfuric acid, and derived sulfuric salts, hydroxide, hydrogen, or proton can gradually replace water and degradation of the tank walls by corrosion will therefore start. Concrete and polymer concrete tank walls can crack due to the additional mechanical constraints imposed by the bath and electrodes and internal stresses while the concrete ages.

Another way of protecting an electrolytic tank from corrosion via the presence of sulfuric acid is to cover an inside of the tank is the use of lead (Pb) liners. U.S. Pat. No. 3,339,266 describes the use of a lead lining on a concrete cell, to hold an electrolyte which is mainly sulphuric acid. The lead lining comprises a bottom sheet, a smaller sheet for a single side wall, and a larger sheet for the other side and two end walls. The sheets are joined by seams formed by welding or burning the lead sheets to connect them. Enhancing corrosion resistance of a tank by lining a surface of the tank walls with lead has also been disclosed in U.S. Pat. No. 2,535,780. U.S. Pat. No. 2,535,780 specifically discloses that a lead sheet for the end walls is brazed to a lead sheet for the side walls to make a water-tight lining for holding the electrolyte in each compartment of the tank.

However, as lead is soft and malleable, sheets liners or bag liners can be prone to damage from impacts of electrodes during hydrometallurgical, maintenance operations, or earthquakes and may also crack while aging. As liners are welded to each corner of the vessel, an empty gap is left between the liner and the tank walls in some regions of the tank. If a crack appears into the liner, sulfuric acid will therefore spread to contact the whole inner surface of the tank walls. Additionally, lead being a metal, such surface treatment of a tank wall can enhance short-circuit problems from anodes to cathodes and losses of current density from one electrolytic cell to another adjacent one.

Providing a hydrometallurgical tank with an anti-corrosive layer presents various challenges that still need to be addressed.

SUMMARY

The present article and related production techniques respond to the above need by providing at least one lead layer solidified onto a portion of the article in contact with a corrosive medium including sulfuric acid. More particularly, the present electrolytic tank design and related production techniques provide at least one lead layer solidified and adhering onto a portion of the cavity defined by the tank walls, thereby formed offering protection against corrosion by the sulfuric acid contained in the cavity. The lead coating techniques described herein provide strength and adherence in comparison to a superposed lead envelope or a regular non-adhesive lead coating which could be applied to the tank walls.

Geometry and thickness of the lead coating are tailored to the tank design to minimize water penetration, sulphuric acid penetration and short-circuit risks while improving its resistance to corrosion. The desired thickness of lead may be obtained by spray-coating one or multiple thin layer(s) of lead on the cavity of the tank. The geometry of the coating may be tailored to provide protection to a portion of the inner surface of the tank walls which is in contact with corrosive fluids of the bath, while avoiding any potential contact with electrically conductive elements from a capping board (equipotential insulator) and contact bar assembly hanging on side walls of the tank.

There is for example provided a corrosion-resistant electrolytic tank including:

-   -   a core defining a cavity to receive a corrosive electrolytic         bath, an external surface of the cavity defining an inner         surface of the tank;     -   a lead coating covering at least a portion of the inner surface         of the tank, the lead coating including at least one layer of         lead being chemically and/or physically bonded to the at least a         portion of the inner surface

In some implementations, the size of the at least a portion of the inner surface is selected according to a level of the electrolytic bath, the configuration of a capping board and contact bar assembly, and on the electrodes hanging bars resting thereon.

There is also provided a process for lead-covering an inner surface of an article defining a cavity in contact with sulfuric acid, the process comprising:

-   -   thermally spraying at least one layer of lead onto the inner         surface of the article to form a sprayed lead coating; and     -   electrodepositing at least one layer of lead onto the sprayed         lead coating to form a lead coating having a minimized porosity.

There is also provided a process for lead-covering an electrolytic tank having an inner surface shaped to hold an electrolytic bath including sulfuric acid, the process including:

-   -   thermally spraying at least one layer of lead onto at least a         portion of the inner surface to form a sprayed lead coating; and     -   electrodepositing at least one layer of lead onto the sprayed         lead coating to form a lead coating having a minimized porosity.

There is also provided a process for lead-covering an electrolytic tank having an inner surface shaped to hold an electrolytic bath including sulfuric acid, the process including:

-   -   coating at least a portion of the inner surface with an         electrically-conductive material to form an         electrically-conductive surface; and     -   electrodepositing at least one layer of lead onto the         electrically-conductive surface to form a lead coating.

There is also provided a process for lead-covering a tank having an inner surface shaped to hold a solution including sulfuric acid, the process including at least one of:

-   -   thermally spraying at least one layer of lead onto at least a         portion of the inner surface; and     -   electrodepositing at least one layer of lead onto the at least a         portion of the inner surface,         to form a lead coating.

There is also provided a process for lead-covering an electrolytic tank having an inner surface shaped to hold an electrolytic bath including sulfuric acid, the process including:

-   -   thermally spraying at least one layer of lead onto at least a         portion of the inner surface to form a lead coating; and     -   applying a corrosion-resistant coating onto the lead coating.

There is also provided a process for manufacturing a corrosion-resistant electrolytic tank, the process including:

-   -   forming an outer envelope and an inner envelope so as to leave a         gap there between and create a space for the formation of the         core;     -   positioning rebars and anchoring systems connectable to         levelling mechanisms and/or lifting accessories within the gap;     -   pouring polymer concrete within the gap to form the core between         the inner envelope and the outer envelope, thereby obtaining a         three-layer structure;     -   curing the three-layer structure at a temperature between 40 and         180° C.; and     -   thermally spraying at least one layer of lead onto at least a         portion of an inner surface of the three-layer structure to         produce the corrosion-resistant electrolytic tank.

There is also provided a process for manufacturing a corrosion-resistant electrolytic tank, the process including:

-   -   forming an outer envelope and an inner envelope so as to leave a         gap there between and create a space for the formation of the         core;     -   pouring polymer concrete within the gap to form the core between         the inner envelope and the outer envelope, thereby obtaining a         three-layer structure;     -   curing the three-layer structure at a curing temperature; and     -   applying at least one layer of lead onto at least a portion of         an inner surface of the three-layer structure to produce the         corrosion-resistant electrolytic tank, applying the at least one         layer of lead being performed according to any one of the         lead-covering processes described herein.

In another aspect, there is provided an electrolytic tank for metal recovery operations, the electrolytic tank having an inner surface defining a cavity to receive a corrosive electrolytic bath including sulfuric acid. The electrolytic tank comprises a corrosion-resistant lead coating covering at least a portion of the inner surface of the tank, the corrosion-resistant lead coating comprising at least one layer of lead being solidified onto the at least a portion of the inner surface of the tank.

In some implementations, a size of the at least a portion of the inner surface is selected according to at least one of the following parameters: a level of the corrosive electrolytic bath, a configuration of a capping board and contact bar assembly, and a configuration of hanging bars resting thereon.

In some implementations, the corrosion-resistant lead coating covers a lower portion of the inner surface of the tank to be contacted with the corrosive electrolytic bath, thereby leaving a remaining portion of the inner surface free from lead.

In some implementations, the electrolytic tank further comprises a core having a base wall and four side walls extending upwardly from an outer edge of the base wall, thereby defining a shape of the cavity, and wherein an inner surface of the core defines the inner surface of the tank.

In other implementations, the electrolytic tank further comprises:

-   -   a core having a base wall and four side walls extending upwardly         from an outer edge of the base wall, thereby defining a shape of         the cavity;     -   an inner hull bonded with an internal surface of the core,         wherein the inner hull defines the inner surface of the tank and         is made of a material having corrosion-resistant properties; and     -   an outer hull bonded with an external surface of the core,         wherein the outer hull is joined to the inner hull at a top         region of the side walls of the core to form an envelope.

In some implementations, the inner hull is made of multiple layers of a fiberglass-based material.

In some implementations, the outer hull is made of multiple layers of a fiberglass-based material.

In some implementations, each layer is fiberglass mat, knitted fiberglass, stitched, stitched-mat, knitted-mat or fiberglass woven roving.

In some implementations, the inner hull has a composition differing from the outer hull. Optionally, thickness of the hulls, type and orientation of the fibers may vary between the inner envelope and the outer envelope.

In some implementations, the at least one layer of lead is derived from a thermal spraying application. Optionally, the thermal spraying application is two-wire electric arc spraying, combustion flame spraying, laser cladding, plasma spraying or HVOF (High Velocity Oxygen Fuel) spraying.

In some implementations, the corrosion-resistant lead coating further comprises a final layer of lead electrodeposited onto the at least one layer of lead, to reduce porosity of the corrosion-resistant lead coating in comparison to that of the at least one thermally sprayed layer alone.

In other implementations, the electrolytic tank further comprises:

-   -   a core having a base wall and four side walls extending upwardly         from an outer edge of the base wall, thereby defining a shape of         the cavity; and     -   an electrically conductive coating applied to at least a portion         of an internal surface of the core that defines the at least a         portion of an inner surface of the tank;         wherein the corrosion-resistant lead coating is derived from         electrodeposition of the at least one lead layer onto the         electrically conductive coating.

In some implementations, the core is made of polymer concrete and the electrically conductive coating is made of a mixture of fiberglass fibers and powdered, flocs, fibers, filaments, or strings of carbon or a metallic material embedded within a cured plastic matrix.

In some implementations, the core is made of polymer concrete and the electrically conductive coating is made of a metallic paint applied to the polymer concrete.

In some implementations, the electrolytic tank further comprises an additional corrosion-resistant coating applied onto the corrosion-resistant lead coating. Optionally, the additional corrosion-resistant coating is at least one of a layer of fiberglass-based material comprising type A and/or Type C fiberglass fibers, and a layer of synthetic fiber. Optionally, the synthetic fiber is polyester. Alternatively, additional corrosion-resistant coating can be made of a thermoplastic resin including Teflon®, Bekaplast® or HDPE.

In another aspect, there is provided an article defining a cavity to receive a corrosive medium, the article comprising:

-   -   at least one layer of a fiberglass-based material defining an         inner surface of the cavity, the fiberglass-based material         having corrosion-resistant properties; and     -   a lead coating covering at least a portion of the inner surface         of the cavity, the lead coating comprising at least one         thermally-sprayed layer of lead being solidified onto the at         least one layer of the fiberglass-based material.

In some implementations, the article can be an electrolytic tank for refining metals, piping, or tubing defining a cavity in contact with acid sulfuric in hydrometallurgical operation, electrowinning operation, electrorefining operation, in solvent extraction operation or in an acid plant operation.

In some implementations, the article can be the electrolytic tank as defined herein.

In another aspect, there is provided a process for manufacturing a corrosion-resistant electrolytic tank defining a cavity receiving a corrosive electrolytic bath including sulfuric acid. The process includes:

-   -   joining an outer hull and an inner hull at at least one         extremity thereof so as to form an envelope defining a gap         between the outer hull and the inner hull, the inner hull being         made of multiple layers of a corrosion-resistant         fiberglass-based material;     -   pouring a concrete-based material within the gap to form a core         between the inner hull and the outer hull, thereby obtaining a         three-layer structure defining a shape of the cavity;     -   curing the three-layer structure at a curing temperature; and     -   applying a lead coating onto at least a portion of an inner         surface of the three-layer structure, the lead coating         comprising at least one layer of lead solidified onto the inner         hull.

In some implementations, applying the lead coating comprises thermally spraying the at least one layer of lead. Optionally, thermally spraying the at least one layer of lead is performed via two-wire electric arc spraying, combustion flame spraying, laser cladding, plasma spraying and HVOF (High Velocity Oxygen Fuel) spraying.

In some implementations, the lead coating further comprises a final layer of lead and applying the lead coating comprises electrodepositing the final layer of lead onto the at least one layer of lead.

In some implementations, the curing temperature is between 40° C. and 180° C.

In some implementations, the process further includes positioning multiple reinforcing pultruded rebars within the gap before pouring the concrete-based material to form the core.

In some implementations, the process further includes positioning multiple anchoring assemblies within the gap before pouring the concrete-based material to form the core, each anchoring assembly comprising a strap and an anchor provided at at least one end of the strap, each anchor offering anchorage from an external surface of the tank to an accessory tailored to levelling, displacement, lifting, operation or maintenance of the tank.

The objects, advantages and other features of the article design and production will become more apparent and be better understood upon reading of the following non-restrictive description, given with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the article, exemplified as a lead-coated tank, are represented in and will be further understood in connection with the following figures.

FIG. 1 is a perspective top view of a tank including a spray-coated lead layer.

FIG. 2 is a top view of the tank of FIG. 1.

FIG. 3 is a cross-sectional view along line III of FIG. 2.

FIG. 4 is a zoomed view of an upper left portion of FIG. 3.

FIG. 5 is a zoomed view of a central lower portion of FIG. 3.

FIG. 6 is a zoomed view of a right lower portion of FIG. 3.

FIG. 7 is a transparent view of the tank of FIG. 1.

FIG. 8 is a schematic drawing of a vertical cross-section of a portion of a side wall of a tank including a core, outer and inner envelopes and a lead coating.

FIG. 9 is a schematic drawing of a vertical cross-section of a portion of a side wall of a tank including a core, an outer envelope and a lead coating.

FIG. 10 is a schematic drawing of a vertical cross-section of a portion of a side wall of a tank including a core, outer and inner envelopes, a lead coating, and an additional corrosion-resistant fiber-containing coating.

FIG. 11 is a schematic drawing of a vertical cross-section of a portion of a side wall of a tank including a core, an outer envelope, a lead coating and an additional corrosion-resistant fiber-containing coating.

FIG. 12 is an exploded perspective view of a tank including a core, outer and inner envelopes, and a lead coating.

FIG. 13 is a semi transparent and cropped view of a portion of a tank showing a core, rebars and anchor systems, outer and inner envelopes, and a lead coating.

FIG. 14 is a top perspective view of a tank including a spray-coated lead layer and additional combined assemblies as contemplated herein.

FIG. 15 is a transparent perspective view of the tank of FIG. 14.

FIG. 16 is a top view of the tank of FIG. 14.

FIG. 17 is a cross-sectional view of the tank of FIG. 16 along line XVII-XVII.

While the present tank will be described in conjunction with example embodiments, it will be understood that it is not intended to limit the scope of the present techniques to these embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included as defined by the appended claims.

DETAILED DESCRIPTION

Hydrometallurgical tanks encompassed herein include tanks of various sizes and shapes used in hydrometallurgical operations for the refining of non-ferrous metals, including precious metals. Tanks may be also referred to as cells or vessels. Any tank having to hold an acidic liquid medium containing sulfuric acid can benefit from the present techniques, thereby encompassing electrolytic tanks containing sulfuric acid from electrolytic baths for performing non-ferrous metal refining by electrolysis, and leaching tanks containing sulfuric acid from leaching baths before refining of precious metals. For example, round tanks used to treat anodic slime and recover precious metals contained therein are also encompassed by the present invention.

In the implementations illustrated in FIGS. 1 and 7, the electrolytic tank (2) includes a rectangular base wall (6) and four side walls (8) extending from peripheral edges of the base wall (6), thereby defining a cavity (9) in which the acidic electrolytic bath can be received. The electrolytic tank (2) is designed to be used in combination with electrodes (anodes and cathodes), and a capping board and contact bar assembly (which are not illustrated in the Figures), thereby forming an electrolytic cell operating for refining non-ferrous metals. The capping board rests on a top surface ((14) in FIG. 4) of a tank side wall and is used to position the electrodes with respect to each other so as to reduce damage to the side walls of the tank during the insertion and removal of the heaving electrodes. The capping board is also used as electric insulator between adjacent tanks and/or adjacent electrodes and/or the ground. Anodes and cathodes are alternately disposed within the electrolytic tank via hanging bars which are resting on the capping board and contacting a contact bar which lays on the capping board. The contact bar is made of a conductive material which transfer electrical current to the hanging bars, and consequently to the electrode.

Referring to FIGS. 1 to 7, the electrolytic tank (2) comprises a protective anti-corrosive coating of lead (10) applied on a portion of the cavity (9) which is in contact with the acidic bath contained therein. The lead coating (10) can offer improved resistance to corrosion by creating a sealing surface upon reaction of lead with sulfuric acid from the acidic bath to form lead sulfate. The number of layers forming the coating, the thickness and geometry of each lead layer may vary and can be adapted according to certain configurations of the tank.

In some implementations, the electrolytic tank can further include at least one additional anti-corrosive layer applied onto the lead coating.

More details with respect to the tank configuration and construction are provided herein.

Core

Referring to FIGS. 1 and 2, the tank (2) can be defined as including a core defined by the base wall (6), and the four side walls (8) extending upwardly from edges of the base wall (6). It should be understood that an inner surface of the core (or tank) defines the cavity (9) receiving the electrolytic bath, and corresponds to the combination of an inner surface of the side walls (8) and a top surface of the base wall (6). An outer surface of the core (or tank) corresponds to the combination of a remaining external surface of the side walls (8) and a bottom surface of the base wall (6).

Optionally, the core can be made of polymer concrete, such as prestressed polymer concrete.

Envelope

In some implementations, the mechanical resistance of the tank walls to internal and external stresses can be improved by the use of a multiple-layer fiberglass-based envelope surrounding the core (16), as seen for example in FIGS. 8 and 10. The envelope (18) can be defined as including an inner hull (180) adhering to the inner surface of the core (16), and an outer hull (182) adhering to the outer surface of the core (16) to enhance stress relief for the concrete polymer of the surrounded core. As seen on FIG. 9, it should be noted that the envelope can only include the outer hull (182), adhering to the outer surface of the core (16).

The envelope can include multiple layers of a fiberglass-based material, that are referred to as multiple fiberglass-based layers and the resulting envelope being referred to as a multiple-layer fiberglass-based envelope or fiberglass-based envelope. The fiberglass-based material is to be understood as a material including fiberglass fibers saturated and bonded with a plastic matrix that can be a thermoset polymer matrix (e.g. epoxy, polyester resin, or vinylester) or a thermoplastic matrix.

Optionally, the multiple-layer fiberglass-based envelope includes multiple layers of at least one of fiberglass mat, knitted fiberglass, stitched, stitched-mat, knitted-mat and fiberglass woven roving. Optionally, the multiple-layer fiberglass-based envelope may include successive layers of at least one fiberglass mat, at least one knitted fiberglass, and at least one fiberglass woven roving. Optionally, the multiple-layer fiberglass-based envelope may include successive layers of fiberglass mat, knitted fiberglass, stitched, stitched-mat, knitted-mat and fiberglass woven roving. Further optionally, a maximum thickness of the multiple-layer fiberglass-based envelope may be between about 8 mm and about 15 mm, optionally 10 mm. It should be understood that the choice of fiberglass-based material for the envelope may depend for example on the desired orientation of the fibers and the size of the tank.

In some implementations, the composition of the inner hull of the envelope can differ from the composition of the outer hull of the envelope. For example, the outer hull can be made of 3 to 7 layers of at least one of fiberglass mat, knitted fiberglass, stitched, stitched-mat, knitted-mat and fiberglass woven roving, and the inner hull can be made of 2 to 5 layers of at least one of fiberglass mat, knitted fiberglass, stitched, stitched-mat, knitted-mat and fiberglass woven roving.

Referring to FIG. 12, the method of constructing the tank can include nesting the inner hull (180) in the outer hull (182) while leaving a gap therebetween. The tank can be built upside down, such that the inner hull and the outer hull are joined at a top surface of the side walls. In some implementations, the inner hull can be joined to the outer hull to form the envelope by bridging extremities of the multiple layers forming the hulls with multiple pieces of fiberglass-based material. The multiple bridging pieces can be overlapping with the multiple layers to be bridged.

If rebars, straps, anchors, connectors, and related assemblies are to be embedded in the tank, the method can include positioning such components into the gap between the inner hull (180) and outer hull (182) and holding them with tools well known in the art (such as studs, laminates or pins). Particularly, the external surface of the components may be ground and chemically treated with silane or adhesives, such as Chemlock® to provide covalent chemical adhesion between the polymer concrete resins and the surface of the components.

The method further includes filling the gap between the inner hull and outer hull, layer by layer, with polymer concrete to create the core (16) which is sandwiched between the two hulls (180,182). The whole tank structure can then be cured, at a temperature between about 40° C. and 180° C.

Protective Multi-Layer Lead Coating

It should be understood that the term “protective” refers to the ability of the lead coating to protect the tank wall from being weakened by corrosion upon contact with sulfuric acid. Lead is known to react with the sulfuric acid contained in the electrolytic bath according to the following equation (I):

Such protection is offered by the formation of lead sulfate PbSO₄, contributing to sealing the tank walls and prevent corrosion thereof by the sulfuric acid.

In comparison to lead liners from the state of the art, such as welded sheet or bag liners, the coating techniques proposed herein ensures bonding and solidification of the lead coating with an external surface of the tank wall. Referring to FIGS. 3 to 6, the desired thickness of lead can be obtained by depositing a layer or multiple layers of lead to form the coating (10) onto a top surface of the base wall (6) (FIG. 5) and the inner surface of the side walls (8) of the tank (FIGS. 4 and 6). The lead deposition techniques proposed herein offer adequate adhesion of the lead coating (10) to the tank walls (6, 8), thereby forming a one-piece structure offering enhanced corrosion resistance.

In the implementations illustrated in FIGS. 1 to 7, and better seen on FIGS. 3 to 5, the protective lead coating (10) can be applied directly onto the polymer concrete of a portion of the inner surface of the core (16). Indeed, as further illustrated in FIGS. 9 and 11, the inner envelope may be omitted when constructing the tank (2) such that the protective lead coating (10) is directly applied onto the inner surface of the core (16) while the outer envelope (182) provides strength to the outer surface of the core (16). In certain conditions, the lead coating (10) can offer sufficient strength and protection via adhesion to the inner surface of the core (16), as the lead can strongly adhere to the polymer concrete according to the deposition technique that is chosen. More details on the deposition techniques are provided below.

In the implementations illustrated in FIGS. 8, 10, 12 and 13, a desired thickness of the protective coating (10) can be applied to at least a portion of the inner hull (180) via a single layer of lead or multiple layers of lead. The protective lead coating (10) offers additional chemical protection and structural strength to the inner hull (180) defining the cavity of the tank. When at least a portion of the inner hull (180) to be in contact with the acidic bath is coated with the protective coating (10), the inner hull (180) can be made thinner than an uncoated inner hull. In addition, referring to FIG. 8, the thickness of the inner hull (180) can be constructed as thin as the outer hull (182). Optionally, referring to FIG. 10, the inner hull (180) can be thinner than the outer hull (182).

The process proposed herein can include thermal spraying of at least one lead layer onto a portion of the cavity (9) of the tank (2), electrodeposition of at least one lead layer onto the portion of the cavity (9), or a combination thereof.

For example, the process can include thermally spraying at least one lead layer onto an external surface of the portion of the cavity (9), and electrodepositing another and final lead layer onto the at least one lead layer which has been thermally sprayed to form the protective lead coating (10) having a given thickness and porosity. Indeed, in certain conditions, thermally sprayed lead layers can be porous and applying a final electrodeposited lead layer can enable further reducing the porosity of the protective lead coating (10). Advantageously, electrodeposition of this additional layer of lead can be performed on site for repairing a damaged lead coating for example. Therefore, the lead coating (10) can be obtained by the superposition of multiple layers of lead applied by different deposition techniques including thermal spraying and electrodeposition.

The at least one thermally sprayed layer is formed by successive impact of a stream of sprayed droplets in fully molten or partially melted state, followed by flattening, rapid cooling and solidification onto the surface of the tank wall (outer hull or core). Thermal spraying techniques includes two-wire electric arc spraying, combustion flame spraying, laser cladding, plasma spraying and HVOF (High Velocity Oxygen Fuel) spraying. Optionally, the spraying technique can be selected to provide a minimized porosity to the resulting lead coating.

In some other implementations, the process can include electrodepositing a first layer of lead onto the inner hull (180) to form the lead coating (10). To achieve electrodeposition of the first layer, the process includes doping the inner hull (180) by adding a conductive material to the combination of resin and fibers forming the inner hull (180). The conductive material can include powdered, flocs, fibers, filaments, and/or strings of carbon or metallic material, including steel, such that at least the surface of the inner hull (180) becomes electrically conductive, allowing electrodeposition of at least a first layer of lead thereon. Alternatively, the process can include applying a metallic paint or a resin layer saturated in non-oxidised metallic particles to a surface of the inner hull (180), such that the surface of the inner hull (180) is electrically conductive, allowing electrodeposition of at least a first layer of lead thereon (formed via electroplating or electrowinning).

The source of lead to be coated can be a powder of pure lead or a lead wire (single strand or multi-strands) in bundle.

In addition, thickness and shape of each lead layer forming the protective coating can vary and be chosen in accordance with the design of the tank and/or of electrodes which will hang therein.

In some implementations, the thickness of each layer of lead forming the protective lead coating can vary from 0.02 to 3 mm, depending on the thermal spraying technique being used, and the total thickness of the protective lead coating may be between about 0.02 and 10 mm.

In some implementations, the protective coating can spread onto a defined portion of the cavity. Referring to FIG. 4, to avoid any potential contact with the hanging bars of the electrodes (not illustrated in FIG. 4), the coating (10) is applied so as to leave an uncoated upper portion (12) of the corresponding inner surface of the tank side wall (8). The coating (10) may end at a distance from a top surface (14) of the side wall (8). The distance can be chosen to ensure that the lead coated portion of the cavity avoids any possible contact with the capping board and hanging bars supported on the tank. The distance can also be chosen to ensure that the uncoated portion of the cavity is not in contact with the electrolytic bath. For example, according to typical electrolytic cell design, the distance can vary between about 5 and about 20 cm, depending on the level of the electrolytic bath, the configuration of capping board and contact bar assembly, and on the electrodes hanging bars resting thereon.

More specifically, the size and shape of the protective lead coating may be selected to limit the risks of conducting the electrical current from the electrodes via the coating because lead is a conductive metallic element. By leaving an upper portion of the cavity uncoated, short circuits can be limited and even prevented. The lead coating is further sized to offer protection against corrosion to at least the portion of the cavity being in contact with the acidic electrolytic bath.

Additional Layers

Referring to the implementations illustrated in FIGS. 10 and 11, an additional corrosion-resistant coating (20), including at least one layer, can be provided onto the protective lead coating (10) of the tank.

Indeed, it should be noted that lead sulfate can be dissolved in concentrated H₂SO₄ by producing acidic salts or complex compounds according to the following equation (II):

PbSO₄(s)+H₂SO₄(conc.)<=>Pb(HSO₄)₂(aq)  (II)

Therefore, when the acidic bath has a high concentration in sulfuric acid, the sealed coating formed upon reaction of the lead (from the lead coating) and sulfuric acid can be further dissolved and corroded, leaving the core of the tank more prone to acidic attacks.

In the implementations illustrated in FIGS. 10 and 11, in presence for example of an acidic bath having sulfuric acid concentration that could lead to dissolution and corrosion of the lead sulfate, the tank can therefore be constructed to include an additional corrosion-resistant coating (20) which is applied onto the protective lead coating (10).

Optionally, the corrosion-resistant coating can include at least one fiberglass layer, containing type A or Type C fiberglass, at least one layer of synthetic fibers, such as polyester, or a combination thereof. Further optionally, a high-performance coating composition including thermoplastic resins with Teflon®, Bekaplast®, HDPE or a combination thereof can be alternatively applied as the corrosion-resistant coating on the lead coating for extra resistance to corrosion in case of contact with highly concentrated sulfuric acid.

Referring to FIG. 10, as the portion of the inner envelope (180) to be in contact with the acidic bath (not illustrated) is coated with the protective coating (10) and the additional corrosion-resistant coating (20), the thickness of such inner envelope (180) may be constructed as thin as the outer envelope (182). Optionally, the inner envelope (180) may be thinner than the outer envelope (182). Optionally, the additional corrosion-resistant coating (20) can have a thickness between about 0.5 mm and about 6 mm.

Multiple layers of the corrosion-resistant material can be superposed to form the corrosion-resistant coating (20). The at least one layer forming the corrosion-resistant coating (20) is baked or cured following standard techniques (via chemical or metallic catalyst, or by ultra-violet (UV) curing, or infrared (IR) curing). Advantageously, the additional corrosion-resistant coating can represent a first barrier to corrosion, while the underneath lead coating is able to react with sulfuric acid and seal the attacked spot when a crack or damage occurs in the corrosion-resistant coating (20).

It should be noted that when a corrosion-resistant coating is applied to the lead protective coating, the lead protective coating can be pre-treated before application of the corrosion-resistant coating. More particularly, the pre-treatment includes reacting the lead protective coating with sulfuric acid to provide further sealing of the protective coating upon formation of PbSO₄. Then, the multiple layers of the corrosion-resistant material can be superposed to form the corrosion-resistant coating onto the pre-treated lead protective coating.

Additional Tank Elements

Further optionally, the core can include a plurality of horizontally and/or vertically extending rebars to further reinforce the structure of the core. The reinforcing rebars can be pultruded and made of fiberglass. Additionally, various anchor assemblies and strap assemblies can be at least partially embedded in the core to provide reinforcement and anchorage points to lifting and anchoring accessories. In the implementation illustrated in FIG. 13, the tank (2) can further comprise one or more flat pultruded rebars (22) that may be embedded within at least two of the four side walls (8). The tank (2) can further include one or more anchor assemblies (24) within at least two of the four side walls (8).

FIGS. 14 to 17 illustrate implementations of a tank assembly 2 including a core, an inner hull, an outer hull, a protective coating and additional reinforcing or levelling elements. FIG. 14 shows levelling assemblies (100) connected to a base wall of the tank to ensure levelling and alignment of the tank with respect to another adjacent tank, for example. FIG. 15 shows a reinforcing grid or mesh (200) embedded in each wall of the core. FIG. 17 shows a pair of anchor assemblies (300) embedded in a side wall (8) of the tank, proximal to an exterior surface thereof, and provided side anchor points (302) to a lifting accessory (not illustrated), for example.

The number and configuration of the rebars may vary as described in the published US Patent Application No. 2018/0148852, incorporated herein by reference. The number and configuration of the anchor assemblies can be as described in published international PCT Patent Application No. PCT/CA2017/050917, international PCT Patent Application No. PCT/CA2019/050106 and international PCT Patent Application No. with adjustable levelling mechanisms, and related levelling assemblies and/or sole assemblies as described in international PCT Patent Application No. PCT/CA2020/050178, incorporated herein by reference.

It should be noted that the present techniques can be applied to a metallic article including a plastic liner, the lead coating offering resistance to corrosion to the liner upon contact with a corrosive medium including sulfuric acid.

It should be noted that any item, article, equipment being in contact with sulfuric acid can benefit from the presently disclosed techniques, including piping, tubing, channels involved in solvent extraction or manufacturing of sulfuric acid in an acid plant or in various industrial processes such as electrorefining or electrowinning of zinc, copper, lead, tin, non-ferrous metals and precious metals.

It should further be noted that the same numerical references refer to similar elements. Furthermore, for the sake of simplicity and clarity, namely so as to not unduly burden the figures with several references numbers, not all figures contain references to all the components and features, and references to some components and features may be found in only one figure, and components and features of the present disclosure which are illustrated in other figures can be easily inferred therefrom. The embodiments, geometrical configurations, materials mentioned and/or dimensions shown in the figures are optional, and are given for exemplification purposes only. Therefore, the descriptions, examples, methods and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only.

In the following description, the term “about” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e. the limitations of the measurement system. It is commonly accepted that a 10% precision measure is acceptable and encompasses the term “about”.

In the above description, an embodiment or implementation is an example of the invention. The various appearances of “one embodiment,” “an embodiment”, “some embodiments”, “some implementations” do not necessarily all refer to the same example. Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. 

What is claimed is:
 1. An electrolytic tank for metal recovery operations, the electrolytic tank having an inner surface defining a cavity to receive a corrosive electrolytic bath including sulfuric acid, and the electrolytic tank comprising: a corrosion-resistant lead coating covering at least a portion of the inner surface of the tank, the corrosion-resistant lead coating comprising at least one layer of lead being solidified onto the at least a portion of the inner surface of the tank.
 2. The electrolytic tank of claim 1, wherein a size of the at least a portion of the inner surface is selected according to at least one of the following parameters: a level of the corrosive electrolytic bath, a configuration of a capping board and contact bar assembly, and a configuration of hanging bars resting thereon.
 3. The electrolytic tank of claim 1, wherein the corrosion-resistant lead coating covers a lower portion of the inner surface of the tank to be contacted with the corrosive electrolytic bath, thereby leaving a remaining portion of the inner surface free from lead.
 4. (canceled)
 5. The electrolytic tank of claim 1, further comprising: a core having a base wall and four side walls extending upwardly from an outer edge of the base wall, thereby defining a shape of the cavity; an inner hull bonded with an internal surface of the core, wherein the inner hull defines the inner surface of the tank and is made of a material having corrosion-resistant properties; and an outer hull bonded with an external surface of the core, wherein the outer hull is joined to the inner hull at a top region of the side walls of the core to form an envelope.
 6. The electrolytic tank of claim 5, wherein the inner hull is made of multiple layers of a fiberglass-based material.
 7. The electrolytic tank of claim 5, wherein the outer hull is made of multiple layers of a fiberglass-based material.
 8. The electrolytic tank of claim 7, wherein each layer is fiberglass mat, knitted fiberglass, stitched, stitched-mat, knitted-mat or fiberglass woven roving.
 9. The electrolytic tank of claim 5, wherein the inner hull has a composition differing from the outer hull.
 10. The electrolytic tank of claim 1, wherein the at least one layer of lead is derived from a thermal spraying application.
 11. The electrolytic tank of claim 10, wherein the thermal spraying application is two-wire electric arc spraying, combustion flame spraying, laser cladding, plasma spraying or HVOF (High Velocity Oxygen Fuel) spraying.
 12. The electrolytic tank of claim 1, wherein the corrosion-resistant lead coating further comprises a final layer of lead electrodeposited onto the at least one layer of lead, to reduce porosity of the corrosion-resistant lead coating in comparison to that of the at least one thermally sprayed layer alone.
 13. The electrolytic tank of claim 1, further comprising: a core having a base wall and four side walls extending upwardly from an outer edge of the base wall, thereby defining a shape of the cavity; and an electrically conductive coating applied to at least a portion of an internal surface of the core that defines the at least a portion of an inner surface of the tank; wherein the corrosion-resistant lead coating is derived from electrodeposition of the at least one lead layer onto the electrically conductive coating.
 14. The electrolytic tank of claim 13, wherein the core is made of polymer concrete and the electrically conductive coating is made of a mixture of fiberglass fibers and powdered, flocs, fibers, filaments, or strings of carbon or a metallic material embedded within a cured plastic matrix.
 15. The electrolytic tank of claim 13, wherein the core is made of polymer concrete and the electrically conductive coating is made of a metallic paint applied to the polymer concrete.
 16. The electrolytic tank of claim 1, further comprising an additional corrosion-resistant coating applied onto the corrosion-resistant lead coating.
 17. The electrolytic tank of claim 16, wherein the additional corrosion-resistant coating is at least one of: a layer of fiberglass-based material comprising type A and/or Type C fiberglass fibers, and a layer of synthetic fiber.
 18. The electrolytic tank of claim 17, wherein the synthetic fiber is polyester.
 19. The electrolytic tank of claim 16, wherein the additional corrosion-resistant coating is made of a thermoplastic resin including Teflon®, Bekaplast® or HDPE.
 20. An article defining a cavity to receive a corrosive medium, the article comprising: at least one layer of a fiberglass-based material defining an inner surface of the cavity, the fiberglass-based material having corrosion-resistant properties; and a lead coating covering at least a portion of the inner surface of the cavity, the lead coating comprising at least one thermally-sprayed layer of lead being solidified onto the at least one layer of the fiberglass-based material.
 21. The article of claim 20, being an electrolytic tank for refining metals, piping, or tubing defining a cavity in contact with acid sulfuric in hydrometallurgical operation, electrowinning operation, electrorefining operation, in solvent extraction operation or in an acid plant operation. 22.-28. (canceled) 